in an interview King was asked, if he could interview god, what would he like it ask, and he said, If he had a son...
If one partner is religous, and the other isn't, but that doesn't matter to either, there shouldn't be a problem, but if one feels strongly about their beliefs or lack of them, it could be a problem. I wouldn't enjoy a partner who attributed everything to a god, good and bad. I consider it signs of maturity or a lack of. Opposites can attract, but can also clash.